#root{
    width: 100px;
    height: 100px;
    background-color: red;
}
#box{
    width: 50px;
    height: 50px;
    background-color: blue;
}
#bg{
    width: 400px;
    height: 300px;
    background-image: url("./assets/img_tree.png");
    background-size: cover;
}